In a radio access network, communication apparatuses of the network generally communicate (with one another, and/or with other communication apparatuses) using radio transmissions that share the same transmission medium (commonly, the surrounding atmosphere). Although such radio transmissions are normally configured to occupy allocated or assigned frequency bands (also called sub-channels, and which may be divided in time to form “chunks”), the radio-frequency spectrum is nevertheless shared by such transmissions.
Radio transmissions occupying the same parts of the shared communication spectrum can interfere with one another. The level of interference will depend on a number of factors, for example on the power levels of the respective transmissions, and on the relative locations of the transmitters. In fact, many factors have an impact on interference.
Considering a radio access network (RAN) comprising base stations (BSs) as an example, these factors include antenna orientation in the BSs, transmission schemes employed (say FDD or TDD) by the BSs, the nature of sectorisation within the cells of the BSs, the power control schemes employed, the handover schemes employed, the nature of traffic being handled by the BSs at each point in time, and the number of active subscribers (e.g. user equipment, or UEs) assigned to each BS at each point in time. Any smart antenna scheme employed in the BSs may also affect interference. Considering the impact of transmission power on interference, it is possible that a BS may be assigned a number of separate sub-channels that may use different transmission power levels. These different power levels can affect interference. Another important factor is the interference leakage between two adjacent sub-channels. Although in telecommunications systems the practical solution is to introduce guard bands to reduce such leakage, the arrangements of sub-channels assigned to a BS can nevertheless affect interference. Other important factors regarding interference may be, for example, surrounding atmospheric conditions and the presence or absence of obstructions to signal propagation. The effect of interference can be signal degradation and an overall drop in system performance as a whole, as compared to that in an “interference-free” system. It is therefore desirable to manage resource allocation or assignment within RANs.
This is particularly the case when a plurality of RANs co-exist, in other words operate at the same time in adjacent or overlapping geographical areas, and frequency spectra. Such multiple RANs may be considered as parts of an overall or total wireless communication system in a geographical region of interest. Efforts are currently being made to improve the abilities of such multiple RANs to co-exist and coordinate themselves; for example the so-called WINNER project.
FIG. 1 shows one way in which multiple RANs can be co-ordinated. Here, an overall system is constituted by a number of Radio Access Networks RAN1, RAN2 and RAN3 which each comprise a Gateway GW for the purpose of accessing the RAN from a higher Core Network CN 6, typically via an IP Network. As proposed in WINNER for example, the GW is responsible for long-term spectrum assignment (see below) and for at least part of the radio resource management (RRM) in its RAN. It is assumed that one GW is assigned for each RAN.
Each RAN may also comprise one or more Base Stations (BS) exemplified in the Figure by BS1, BS2, BS3, each of which is connected to at least one GW. Each such BS may transmit (and receive) radio signals to (and from) one or more User Equipments (UEs), within its geographical area of coverage (often referred to as a “cell”). UEs may also be referred to as user terminals (UTs), terminal equipments (TEs) or Mobile Stations (MSs). Since both base stations and user terminals are equipped to transmit and receive signals over one or more of the RANs, they are sometimes referred to below collectively as transceivers. As explained in more detail below, base stations and their UEs may be grouped into “clusters” extending over one or more adjacent or even non-adjacent cells, for spectrum allocation purposes.
Communications between the CN, GWs and BSs may be across wired communication links (e.g. via fiber-optic links) or across wireless communication links (e.g. across radio or microwave links). As indicated by arrows in FIG. 1, the GWs communicate among themselves, for example for the purpose of long-term (LT) spectrum assignment, as will be explained later. Meanwhile, the BSs communicate among themselves for, among other things, short term (ST) spectrum assignment as will also be explained below. Communications between the BSs and the UEs are typically across wireless links.
The CN may be distributed, for example across the IP network. The IP network may, for example, include the Internet. Although three RANs are shown in FIG. 1, the network may include any number of such RANs. Similarly, each RAN may have any number of GWs, BSs and UEs. The UEs may be mobile and move from the cell of one BS to that of another BS, and even from one RAN to another RAN. The BSs may be dedicated to a particular RAN, or may be shared between RANs on a temporary or non-temporary basis. One BS may for example serve two RANs at the same time. Although the RANs in FIG. 1 are made up of the same component apparatuses, they may employ different radio access technologies. Typically, different RANs may be operated by different mobile-network operators. Different RANs and BSs may have separate geographical areas of coverage, or may have partially or fully-overlapping areas of coverage. For example, one RAN may effectively be co-located with another RAN, perhaps by siting their respective base stations at the same sites or in the same housings.
The above is only one general type of radio access network. In this specification, the term radio access network or RAN also encompasses a wireless sensor network (WSN) in which the nodes are sensors of some kind, configured to at least act as transmitters (and sometimes also act as receivers). One special form of wireless sensor network is a so-called Body Area Network or BAN, in which sensors are placed at one or more positions on or in living bodies for the purpose of monitoring medical parameters or bodily activity. Two forms of BAN are MBAN or Medical BAN for use in hospitals and other health-related applications, and Wireless BAN or WBAN, this more general designation also extending to security applications for example.
The sharing of radio frequency spectrum in such networks is of particular concern, given the intense proliferation of UE usage in recent years, and the expected increase in the number of UEs in circulation in the near future. In this respect, the requirements of radio systems are changing. While some systems and mobile operators may starved of spectrum resources, most of the existing radio spectrum resources may remain under-utilised or unused most of the time. In the design of wireless radio infrastructure, as in WINNER for example, it is therefore desirable to attempt to share the already existing spectrum in a way which would ultimately lead to better utilisation, thereby solving the problem of poor utilisation of spectrum in the presence of an increasing demand for wireless connectivity. One aspect of such spectrum sharing is to identify so-called “white spaces” in time, frequency and space which are not currently occupied by one RAN, allowing another RAN to transmit in these white spaces.
However, given the potential for interference as already noted, interference management, also referred to below as interference mitigation, is essential for allowing efficient sharing and utilization of spectrum between co-existing RANs.
The concept of “interference temperature” has been proposed for use in managing interference between different RANs. This concept uses the fact that it is the interference level at the affected receiver, rather than at the transmitter causing the interference, which is important to determine the impact of a transmission on other networks. By limiting the total interference experience at a given receiver, it is possible to allow transmitters to operate in frequency bands (sub-channels or chunks) already allocated to other RANs whilst protecting those other networks from undue interference. In practice, it is unrealistic to expect each transmitter to obtain the necessary information for estimating how their emissions would affect the interference temperature of nearby receivers. Nevertheless, the concept of “interference temperature” is useful for classifying the level of interference experienced in particular frequency bands by receivers and groups (e.g. clusters) of receivers.
Efficient coordination between interference control agents in co-existing RANs can contribute to a better quality-of-service (QoS) across all the involved RANs. The inventor of the present invention has recently proposed a semi-distributed cluster wide approach for dynamic channel allocation and so-called gateway centralised interference mitigation to permit efficient interference management within a RAN. However, an outstanding problem is that on some occasions any one GW in isolation might be unable to have full control on interference inflicted on its own RAN from other RANs. The reason for this is that it can only control the sub-channel allocation in its own RAN, and has no influence on other RANs' interference mitigation and sub-channel allocation processes. It is desirable to overcome this shortcoming by providing efficient methods for a GW-to-GW coordination for an efficient interference mitigation and radio sub-channel allocation.